The present invention relates to a variable valve operating system of an internal combustion engine enabling valve-lift characteristic (valve lift and event) and phase to be varied, and in particular being capable of continuously simultaneously changing all of valve lift, working angle, and phase of intake and/or exhaust valves depending on engine operating conditions.
There have been proposed and developed various internal combustion engines equipped with a variable valve operating system enabling valve-lift characteristic (valve lift and lifted period) and phase to be varied depending on engine operating conditions, in order to reconcile both improved fuel economy and enhanced engine performance through all engine operating conditions. One such variable valve operating system with variable valve-lift characteristic and phase control device has been disclosed in Japanese Patent Provisional Publication No. 2000-220420 (hereinafter is referred to as JP2000-220420). The variable valve operating system disclosed in JP2000-220420 is comprised of a variable valve-lift characteristic mechanism (exactly, a two-stage valve-lift and working angle control mechanism) and a variable phase control mechanism. The two-stage valve-lift and working angle control mechanism is capable of changing from one of a large valve-lift characteristic and a small valve-lift characteristic to the other by switching an active cam from one of a high speed cam and a low speed cam to the other. On the other hand, the variable phase control mechanism is capable of advancing or retarding a phase of working angle. The two-stage valve-lift and working angle control mechanism and the variable phase control mechanism are hydraulically operated independently of each other by means of respective hydraulic actuators. Such two-stage switching between the small and large valve-lift characteristics cannot adequately cover a wide range of engine operating conditions. In case of the two-stage switching between only two valve-lift characteristics, it is impossible to vary a valve lift characteristic over a wide range of valve lift characteristics containing a small lift and working angle suited to reduced fuel consumption in steady-state driving, a somewhat large valve lift and working angle suited to improved engine performance at full throttle and low speed, and a large valve lift and working angle suited to improved engine performance at full throttle and high speed. In recent years, for high-precision engine control, there have been proposed and developed various variable valve operating systems enabling valve-lift characteristic (valve lift and working angle) to be continuously simultaneously varied depending on engine operating conditions. One such continuous variable valve-lift characteristic mechanism has been disclosed in Japanese Patent Provisional Publication No. 11-107725 (hereinafter is referred to as JP11-107725). The continuous variable valve-lift characteristic mechanism as disclosed in JP11-107725 is often combined with the previously-noted variable phase control mechanism so as to construct a continuous variable valve-lift characteristic and phase control system. In order to accurately and continuously control both the continuous variable valve-lift characteristic mechanism and the variable phase control mechanism combined with each other, three major components are employed with the continuous variable valve-lift characteristic and phase control system. These are (i) sensors that detect actual control states of the respective mechanisms, (ii) actuators for the two mechanisms, and (iii) an electronic controller or an electronic control unit (ECU) or an electronic control module (ECM) that controls each actuator so that the value of the controlled quantity for each mechanism is brought closer to a desired value.
Actually, sampling of the control state is executed every predetermined sampling time intervals. Assuming that the sampling time interval is fixed to a constant time length irrespective of engine speeds and additionally the fixed sampling time interval is suited to low engine speeds, there is an increased tendency for the controllability to be deteriorated during high-speed operation. If such a fixed sampling time interval suited to the low engine speeds is used for an internal combustion engine whose intake air quantity can be controlled by way of variable intake-valve lift characteristic control, the intake-air quantity control accuracy may be lowered, thus deteriorating combustion stability. In contrast to the above, assuming that the sampling time interval can be changed depending upon an engine speed so as to provide a sampling time interval suited to high engine speeds, for example, if the sampling time interval can be changed to a short sampling time interval suited to high engine speeds, there is a problem of a large control load on the continuous variable valve-lift characteristic and phase control system during high-speed operation.
Accordingly, it is an object of the invention to provide a variable valve operating system of an internal combustion engine enabling valve-lift characteristic and phase to be continuously varied, which avoids the aforementioned disadvantages.
In order to accomplish the aforementioned and other objects of the present invention, a variable valve operating system of an internal combustion engine comprises a variable lift and working angle control mechanism that enables both a lift and a working angle of an engine valve to be continuously simultaneously varied depending on engine operating conditions including at least an engine speed, a variable phase control mechanism that enables a phase at a maximum valve lift point of the engine valve to be varied depending on the engine operating conditions, a first sensor that detects an actual control state of the variable lift and working angle control mechanism every sampling time intervals, a second sensor that detects an actual control state of the variable phase control mechanism every sampling time intervals, at least one of the sampling time interval for the first sensor and the sampling time interval for the second sensor having a characteristic that the one sampling time interval varies relative to the engine speed, and a rate of change in the sampling time interval for the first sensor with respect to the engine speed being different from a rate of change in the sampling time interval for the second sensor with respect to the engine speed.
According to another aspect of the invention, an internal combustion engine comprises a variable lift and working angle control mechanism that enables both a lift and a working angle of an engine valve to be continuously simultaneously varied depending on engine operating conditions including at least an engine speed, a variable phase control mechanism that enables a phase at a maximum valve lift point of the engine valve to be varied depending on the engine operating conditions, engine sensors that detect the engine operating conditions, a first sensor that detects an actual control state of the variable lift and working angle control mechanism every sampling time intervals, a second sensor that detects an actual control state of the variable phase control mechanism every sampling time intervals, a first actuator that provides a motive power to the variable lift and working angle control mechanism, a second actuator that provides a motive power to the variable phase control mechanism, a control unit configured to be electronically connected to the engine sensors, the first and second sensors, and the first and second actuators, for feedback-controlling all of the lift, the working angle, and the phase of the engine valve depending on the engine operating conditions, the control unit comprising a data processor programmed to perform the following,
(a) calculating a desired control state of the variable lift and working angle control mechanism and a desired control state of the variable phase control mechanism based on the engine operating conditions;
(b) calculating both a set value of a first sensor counter corresponding to the sampling time interval for the first sensor and a set value of a second sensor counter corresponding to the sampling time interval for the second sensor based on the engine speed;
(c) sampling the actual control state of the variable lift and working angle control mechanism each time the set value of the first sensor counter has expired;
(d) sampling the actual control state of the variable phase control mechanism each time the set value of the second sensor counter has expired;
(e) applying an error signal corresponding to a deviation of the actual control state of the variable lift and working angle control mechanism from the desired control state to the first actuator; and
(f) applying an error signal corresponding to a deviation of the actual control state of the variable phase control mechanism from the desired control state to the second actuator;
a rate of change in the sampling time interval for the first sensor with respect to the engine speed being different from a rate of change in the sampling time interval for the second sensor with respect to the engine speed.
According to a further aspect of the invention, an internal combustion engine comprises a variable lift and working angle control means for enabling both a lift and a working angle of an engine valve to be continuously simultaneously varied depending on engine operating conditions including at least an engine speed, a variable phase control means for enabling a phase at a maximum valve lift point of the engine valve to be varied depending on the engine operating conditions, engine sensor for detecting the engine operating conditions, a first sensor for detecting an actual control state of the variable lift and working angle control means every sampling time intervals TS1, a second sensor for detecting an actual control state of the variable phase control means every sampling time intervals, a first actuator for providing a motive power to the variable lift and working angle control means, a second actuator for providing a motive power to the variable phase control means, a control unit configured to be electronically connected to the engine sensors, the first and second sensors, and the first and second actuators, for feedback-controlling all of the lift, the working angle, and the phase of the engine valve depending on the engine operating conditions, the control unit comprising a data processor programmed to perform the following,
(a) calculating a desired control state of the variable lift and working angle control means and a desired control state of the variable phase control means based on the engine operating conditions;
(b) calculating both a set value of a first sensor counter corresponding to the sampling time interval for the first sensor and a set value of a second sensor counter corresponding to the sampling time interval for the second sensor based on the engine speed;
(c) sampling the actual control state of the variable lift and working angle control means each time a count value of the first sensor counter reaches the set value;
(d) sampling the actual control state of the variable phase control means each time a count value of the second sensor counter reaches the set value;
(e) applying an error signal corresponding to a deviation of the actual control state of the variable lift and working angle control means from the desired control state to the first actuator;
(f) clearing the count value of the first sensor counter after application of the error signal to the first actuator;
(g) applying an error signal corresponding to a deviation of the actual control state of the variable phase control mechanism from the desired control state to the second actuator; and
(h) clearing the count value of the second sensor counter after application of the error signal to the second actuator;
a rate of change in the sampling time interval for the first sensor with respect to the engine speed being different from a rate of change in the sampling time interval for the second sensor with respect to the engine speed.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.